This invention relates to an apparatus for measuring the temperature of the coolant flowing in the reactor core of a nuclear reactor, a method for measuring the temperature of the coolant and an apparatus for monitoring a nuclear reactor.
In the boiling water reactor, a neutron detector is inserted into the reactor core from the bottom. To calibrate the sensitivity of the neutron detector, it has been proposed to combine a γ-ray thermometer and a neutron detector to observe the thermal power distribution of the nuclear reactor of the boiling water reactor (see Japanese Patent Publication No. 3556409 (the entire contents of which are incorporated herein by reference)).
A γ-ray thermometer is designed to measure the temperature difference within a detector due to the exothermic phenomena in the structural member attributable to γ-rays by a differential thermocouple. Since the amount of heat generation due to γ-rays is proportional to the thermal power of the nuclear reactor, it is possible to observe the axial thermal power distribution of the nuclear reactor by installing and arranging a plurality of detectors of γ-ray thermometers in the axial direction. Similarly, it is possible to observe the horizontal thermal power distribution of the nuclear reactor by installing and arranging a plurality of γ-ray thermometers at various horizontal positions.
A normal γ-ray thermometer contains a calibration heater so as to calibrate a differential thermocouple of a γ-ray thermometer by providing electricity to the calibration heater. By one of the methods for calibrating sensitivity with a calibration heater, the sensitivity is determined from the amount of emitted heat generated by the calibration heater and the change in the output signal of the differential thermocouple.
Meanwhile, although the temperature of the coolant flowing in the reactor core of a boiling water reactor is an important parameter for computationally evaluating the performance of the reactor core, the temperature indirectly observed at the coolant piping located outside the reactor is used for computationally evaluating the performance of the reactor core conventionally.
Conventional boiling water reactors do not have any means for directly observing the temperature of the coolant flowing in the reactor core that is an important parameter for computationally evaluating the performance of the reactor core. This lack of direct observation means is an error factor for computationally evaluating the performance of the reactor core. However, to install an in-core thermometer in order to observe the temperature of the reactor core coolant, it is necessary to modify the design of the existing reactor vessel. So, the design modification of the existing reactor vessel causes large increase of cost and is not a realistic choice.
Therefore, it is an object of the present invention to make it possible to directly observe the temperature of the coolant flowing in the reactor core in the nuclear reactor and monitor the nuclear reactor without modifying the design of the reactor vessel.